- 1. Zero is a number.
- 2. If is a number, the successor of is a number.
- 3. Zero is not the successor of a number.
- 4. Two numbers of which the successors are equal are themselves equal.
- 5. (Induction Axiom.) If a set of numbers contains Zero and also the successor of every number in , then every number is in .

© 1996-9

1999-05-26